Described below are a method and a device for monitoring a web speed of a material web moved by rollers.
Material web is to be understood as meaning a web of flat material, e.g. of paper, plastic or metal.
In machines having continuous material webs moved by rollers, the circumferential speeds of the driving rollers and the related web speed of the material webs must be monitored. In particular, two speed threshold values must be taken into account: a maximum mechanical web speed which must not be exceeded in order to prevent damage to the machine, and a so-called safe speed which allows the operators to enter hazardous areas while the machine is in motion, e.g. to carry out maintenance work.
DE 44 30 550 A1 discloses a method for controlling web speeds in a device for transporting an elastic material web or stretching a plastically deformable material web, wherein the transporting or stretching is accomplished by electric drives in rotational speed control circuits. From a master speed of the material web and the respective elongation, associated web speed target values are determined from which a target rotational speed for the rotational speed control circuit is determined using the diameters of rollers connected to the drives and possibly by gear ratios.
DE 101 04 795 A1 discloses target value correction for an electrically open- or closed-loop controlled slave axis which follows a master movement of a higher-order master axis according to a predefined functional relationship. A respective actual position value of the master axis for controlling the slave axis is increased by a position correction value.
DE 26 13 600 A1 discloses a rotational speed control system for a web-conveying machine, wherein rotational speed controllers for rolls having identical diameters have identical rotational speed target values predefined for them, and suitable rotational speed target values which are corrected by strip tension controllers are provided for rolls or more precisely groups of rolls having a diameter at variance with a master roll diameter.
DE 692 02 132 T2 discloses a drive system for web conveyors with a drive roller device having a plurality of web drive rollers each having an independent motor drive linked to the drive rollers, wherein each motor drive has a way to produce an output signal corresponding to its respective motor drive current.